Assg: ALL
Name
Lab: Enzyme Catalysis
Date
pd.
OBJECTIVES:
Before doing this lab you should understand:
 The general functions and activities of enzymes;
 In general, how environmental changes (changes in temperature, pH, enzyme concentration, and substrate
concentration) might affect the reaction rates and efficiency of enzyme-catalyzed reactions.
After doing this lab you should be able to:
 Measure and explain the effects of changes in enzyme and substrate concentration on reaction rates of an
enzyme catalyzed reaction in a controlled experiment.
 Be able to graph and interpret results of the experiment.
INTRODUCTION: What would happen to your cells if they made a poisonous chemical? You might think that they would
die. In fact, your cells are always making poisonous chemicals. They do not die because your cells use enzymes to break
down these poisonous chemicals into harmless substances. Enzymes are proteins that speed up the rate of reactions
that would otherwise happen more slowly. The enzyme is not altered by the reaction. You have hundreds of different
enzymes in each of your cells.
Each of these enzymes is responsible for one particular reaction that occurs in the cell. In this lab, you will study an
enzyme that is found in the cells of many living tissues. The name of the enzyme is catalase (KAT-uh-LAYSS); it speeds up
a reaction which breaks down hydrogen peroxide, a toxic chemical, into 2 harmless substances--water and oxygen.
The reaction is as follows: 2H2O2 ----> 2H2O + O2 (fix)
This reaction is important to cells because hydrogen peroxide (H2O2) is produced as a byproduct of many normal cellular
reactions. If the cells did not break down the hydrogen peroxide, they would be poisoned and die. In this lab, you will
study the catalase found in chicken liver cells. It might seem strange to use dead cells to study the function of enzymes.
This is possible because when a cell dies, the enzymes remain intact and active for several weeks, as long as the tissue is
kept refrigerated.
Some chemical reactions that make life possible are too slow or have activation energies (the energy needed to start a
reaction) that are too high to make them practical for living tissue. Therefore, the use of catalyst allows these reactions
to take place.
In an enzyme-catalyzed reaction, the substance to be acted upon (the substrate = S) binds reversibly to the active site
of the enzyme (E). One result of this temporary union is a reduction in the energy required to activate the reaction of
the substrate molecule so that the products (P) of the reaction are formed.
In summary:
E+S
➔
ES
➔ E+P
(ES is called the enzyme-substrate complex)
Note that the enzyme is not changed in the reaction and can be recycled to break down additional substrate
molecules. Each enzyme is specific for a particular reaction because its amino acid sequence is unique and causes it
to have a unique three dimensional structure. The active site is the portion of the enzyme that interacts with the
substrate, so that any substance that blocks or changes the shape of the active site affects the activity of the
enzyme.
The primary reaction catalyzed by catalase is the decomposition of H2O2 to form water and oxygen:
2 H2O2 ➔ 2 H2O + O2 (gas)
In the absence of catalase, this reaction occurs spontaneously, but very slowly. Catalase speeds up the reaction
considerably. In this experiment, the rate of reaction will be indirectly measured. The assay system used in this lab
consists of a filter paper disk that is coated with the enzyme and then dropped into a cup of substrate (hydrogen
peroxide). As the catalyst breaks down the hydrogen peroxide into water and oxygen gas, the bubbles of oxygen
collect underneath the filter paper disk and make it rise to the surface of the hydrogen peroxide. The time it takes for
the filter paper disk to rise (from the bottom of the cup) is an indication of the rate of enzyme activity.
I.
II.
III.
__________________________: How does environmental changes (changes in temperature, enzyme
concentration, and substrate concentration, etc) affect the reaction rates and efficiency of enzyme-catalyzed
reactions.
__________________________:
__________________________
1. __________________________: (see lab table)
2. __________________________: (see lab table)
Changing the substrate ____________________: (see lab table for detailed instructions)
Changing the catalase ____________________: (see lab table for detailed instructions)
More procedure:
Changing the temperature ____________________: (see lab table for detailed instructions)
More procedure:
Changing the substrate _______________
Trail
Height
Time
Rate
Substrate at 3%
1
2
3
Average 
Substrate at 2%
1
2
3
Average 
Substrate at 1%
1
2
3
Average 
Changing the catalase_________
Height
Time
Rate
Catalase 75%
Changing the temperature
Height
Time
Rate
Warm water
Average 
Catalase 50%
Average 
Room temperature
Average 
Catalase 25%
Average 
Cold water
Average 
Average 
Average Rates
Groups
3% H2O2
2% H2O2
1% H2O2
________
degrees
________
degrees
________
degrees
1
2
3
4
5
6
7
8
___% catalase
___% catalase
___% catalase
Title:____________________________________________________________________
Key for bar graph
V.
________________________________________
1. Summarize the impact of hydrogen peroxide concentration on the rate of reaction.
2. What was the independent variable?
3. What was the dependent variable?
4. Summarize the impact of enzyme concentration on the rate of reaction.
5. What was the independent variable?
6. What was the dependent variable?
7. Summarize the impact of temperature on the rate of reaction.
8. What was the independent variable?
9. What was the dependent variable?
10. Summarize the impact of pH on the rate of reaction.
11. What was the independent variable?
12. What was the dependent variable?
13. What other situation can affect the rate of reaction?
14. Design that experiment.